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	<PARAM NAME="Keyword" VALUE="Approach locking">
	<PARAM NAME="Keyword" VALUE="Route locking">
	<PARAM NAME="Keyword" VALUE="Locking of routes">
	<PARAM NAME="Keyword" VALUE="Route truncation">
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<P><B><A NAME="6.2"></A>6.2  Approach locking</B></P>

<P>If a route is attempted to be cancelled in front of an approaching train (i.e. within three non-red running signals - i.e. not ground signals - of a train that is protected by the route), or is occupied by a moving train, then a warning is given that the route will be locked if cancellation proceeds.  In this case all signals on the locked section change immediately to red, but the route remains in place in order to protect the trains (no other conflicting routes may be set while it remains in place).  It will remain locked for a period of two minutes to allow all relevant trains to come to a stop.  Locked routes are marked with crosses over the locked section.  A route that is locked by the signaller incurs a performance penalty in that it makes SPADs (signals passed at danger) more likely. If a train is running on an unprotected section of track before reaching a route, then that route may be cancelled immediately because the route is not protecting the train.</P>

<P>Routes that are locked cannot be truncated.</P>

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